This invention relates generally to CCD (charge coupled device) imaging and particularly to a method for detecting blemishes in the proximity of the perimeter of an image on a CCD.
U.S. Pat. No. 4,454,545 issued to R. A. Duschl discloses a CCD based inspection system.
U.S. Pat. No. 4,454,541 issued to R. A. Duschl discloses a system and method for detecting blemishes on the screen of a kinescope. Blemishes are detected by comparing the signal level on each CCD pixel with the average of the signals on the immediately adjacent pixels and generating a blemish signal when the difference exceeds a predetermined threshold.
U.S. Pat. No. 4,575,751 "Method and Subsystem for Plotting The Perimeter of an Object" filed Nov. 15, 1983 by R. A. Duschl discloses a system for plotting the perimeter of an image cast onto a CCD. The image pixels immediately adjacent to the perimeter pixels are identified and their addresses held in memory irrespective of the orientation of the image and the size of the image.
U.S. Pat. No. 4,605,960 entitled "Method for Avoiding Identifying Perimeter Variations As Blemishes In A CCD Image" filed Oct. 22, 1984 by Edward Cohen discloses a method which can be used along with the present invention.
U.S. application Ser. No. 663,153 entitled "Method For Detecting Blemishes Near The Perimeter Of A CCD Image" filed Oct. 22, 1984 by Edward Cohen, discloses a method for detecting blemishes contiguous to a perimeter plotted by the system disclosed in R. A. Duschl U.S. Pat. No. 4,575,751.
The above patents and applications are incorporated herein by reference.
The systems described in the above-referenced applications and patents are quite satisfactory for the purposes intended. However, difficulties sometimes arise because in some instances the light which passes through the image in the proximity of the perimeter is substantially lower than that in the center of the image. The method described in applicaton Ser. No. 663,153 detects blemishes which are contiguous with the perimeter of the object being inspected. This method is not effective in detecting blemishes near to, but spaced from, the perimeter. For these reasons, there is a need for a method of detecting blemishes near an image perimeter which is different from the method used in the center of the image. The present invention fulfills this need.
The present invention is cast into the environment of detecting the perimeter of a black matrix on the inside surface of a CRT faceplate panel. This environment was selected when describing the present invention because the invention is used along with the inventions described in the referenced patents and patent applications and those inventions are described in that environment. Nevertheless it will be understood by those skilled in the art that the present invention is useful in detecting blemishes in the proximity of the perimeter of any image cast onto a CCD.